Hydraulic regenerative drive system and controls

Abstract

The hydraulic regenerative drive system for a vehicle includes an electronic controller, a hydraulic control circuit that receives control signals from the electronic controller, a reservoir in fluid communication with the hydraulic control circuit, a pump/motor unit having a controlled-angle swash plate element providing variable displacement, an accumulator in fluid communication with the hydraulic control circuit and a pump/motor unit speed sensor and pump/motor unit pressure sensor providing measured speed and measured pressure signals to the electronic controller. The electronic controller generates a torque signal and a modified engine throttle signal on the basis of a mathematical model, converts the torque signal to a swash plate angle, and controls a controlled-torque retard mode of operation and a controlled torque propulsion mode of operation. The electronic controller also performs a conversion between the torque signal and swash plate angle on the basis of searching predetermined characteristics of torque versus pressure versus speed.

1. A hydraulic regenerative drive system for a vehicle comprising:
 an electronic controller receiving a nominal engine throttle signal, generating a time-variant torque signal therefrom, and outputting a modified engine throttle signal, and wherein said torque signal and the vehicle's engine torque corresponding to the modified throttle signal are equal to the torque corresponding to the nominal engine throttle signal; 
 a hydraulic control circuit receiving controlling signals from the electronic controller; 
 a reservoir in fluid communication with said hydraulic control circuit for storing hydraulic fluid; 
 a pump/motor unit having a controlled-angle swash plate element providing variable displacement said pump/motor unit being in fluid communication with said hydraulic control circuit and adapted for connection to the drive train of a vehicle; 
 an accumulator in fluid communication with said hydraulic control circuit; 
 a pump/motor unit speed sensor and a pump/motor unit pressure sensor providing measured speed and measured pressure signals to the electronic controller; 
 wherein said electronic control further generates said torque signal and said modified engine throttle signal on the basis of a mathematical model of drive train elements between the engine of said vehicle and said drive train connection-point of said pump/motor unit, converts said torque signal to a swash plate angle, and controls (i) a controlled-torque retard mode of operation, in which said swash plate angle is controlled by said torque signal to impart a dynamically calculated retarding torque to said drive train, and said pump/motor unit pumps fluid from said reservoir to said accumulator via said hydraulic control circuit, and (ii) a controlled-torque propulsion mode of operation, in which said swash plate angle is controlled by said torque signal to impart a dynamically calculated propelling torque to said drive train, and said pump/motor unit motors under influence of fluid from said accumulator passing to said reservoir via said hydraulic control circuit; and 
 wherein said electronic controller performs said conversion between said torque signal and swash plate angle on the basis of searching predetermined characteristics of torque versus pressure versus speed for a set of swash plate angles to locate one or more closest torque values for the predetermined pressure and speed closest to the measured pump/motor unit pressure and pump/motor unit speed, and deriving a swash plate angle from the angle values corresponding to said closest torque values. 
 
   
   
     2. The system according to  claim 1 , wherein said electronic controller further controls a standby mode of operation in which said pump/motor unit neither pumps nor drives, and further wherein said electronic controller enables said retard mode to occur only as a transition from said standby state, and enables said propulsion mode to occur only as a transition from said standby state. 
   
   
     3. The system according to  claim 2 , wherein said electronic controller further controls transition states between said modes, including:
 a pre-propulsion state between standby mode an propulsion mode in which said controller determines that said pump/motor unit pressure exceeds a threshold value before causing said propulsion mode to occur; and 
 a pre-retard state between standby mode and retard mode in which said controller determines that said pump/motor unit pressure is lower than a threshold value before causing said retard mode to occur. 
 
   
   
     4. The system according to  claim 3 , wherein said transition states further include:
 a terminate propulsion state between propulsion mode and standby mode; 
 a terminate retard state between retard mode and standby mode; 
 and wherein said electronic controller further determines in said transition states that respective elements of said hydraulic control circuit have correctly changed condition in response to said controlling signals before causing a respective mode to occur.